This invention relates to a system applying anaerobic contact processing for the treatment of waste, e.g., wastewater.
In general, two categories of biological processes are available for wastewater treatment: aerobic processes and anaerobic processes. Aerobic processes utilize bacteria which require oxygen to convert organic materials primarily to water and carbon dioxide. Anaerobic processes, on the other hand, utilize bacteria which grow in the absence of oxygen and convert organic materials primarily to the end products methane and carbon dioxide. It has been found that for high strength wastewaters, that is wastewaters having a Chemical Oxygen Demand (COD) greater than 2000 mg/L, anaerobic processes are more advantageous because (1) they require less energy and (2) they produce between one-tenth and one-fifth of the residual biomass resulting from aerobic processes.
With respect to the treatment of high strength wastewaters having a Total Suspended Solid (TSS) level greater than 500 mg/L, two categories of anaerobic processes are effective. The first anaerobic process category utilizes anaerobic lagoons which exist as large pits or vessels. With anaerobic lagoons, wastewater is simply introduced into one end of the lagoon whereby suspended anaerobic bacteria within the lagoon degrade both dissolved and particulate organic materials. After an average retention time of several weeks, treated wastewater flows from the anaerobic lagoon.
A second anaerobic process category for wastewater treatment is anaerobic contact processing. Anaerobic contact processes utilize a flow-through, closed top reacting vessel containing anaerobic bacteria. Wastewater flowing into the reacting vessel interacts with the anaerobic bacteria, forming an anaerobic liquor. The anaerobic liquor subsequently flows to a settling vessel or clarifier wherein the bacterial solids settle to the bottom of the settling vessel, leaving the relatively clean wastewater to overflow from the top of the settling vessel. Settled solids are then pumped back to the reactor and the process is continued. Before entering the clarifier, the anaerobic liquor passes through a degassifier to minimize the occurrence of super-saturated gases. A typical problem with the anaerobic contact process, however, is achieving good gravity separation of the bacteria from the anaerobic liquor under atmospheric conditions so that only relatively clean wastewater is decanted from the settling vessel.
Several embodiments exist for applying anaerobic processes, a more recent embodiment is the anaerobic sequencing batch reactor (ASBR). An ASBR operates by partially filling a reactor vessel containing anaerobic bacteria with wastewater and gently mixing the contents so to assist the anaerobic bacteria in degrading the organic materials of the wastewater. After the anaerobic bacteria react with the wastewater, the mixer is turned off, allowing the anaerobic bacteria to settle to the bottom of the reactor vessel. The treated wastewater is then decanted from the top of the reactor vessel. Limitations, however, of this anaerobic process are (1) the need for a relatively large feed equilization to accommodate the batch operation and 2) the need to provide a variable-level tank, decanter, and gas collection system.
For wastewaters having a TSS greater than 500 mg/L, lagoons and anaerobic contact processing systems are more effective in treatment. Lagoons, however, require large land space while anaerobic contact systems are subject to settling problems resulting from inadequate degassification or even regassification in the clarifier. An anaerobic contact system is also costly because it requires multiple components: i.e., a separate equalization reactor, a degassifier, outdoor clarifier vessels, associated return pumps, and piping.
The inventor of the invention described herein has developed an apparatus which modifies the conventional application of the anaerobic contact process. Use of this invention precludes the degassification problems occurring in the clarifier device associated with the conventional anaerobic contact process without requiring batch operation or variable-level operation. Additionally, the invention described herein can be manufactured and used at a cost which is much less than that required for an apparatus applying the conventional anaerobic contact process.
The present invention is directed to an apparatus and method of using the apparatus for treatment of wastewater. With respect to the invention described herein, wastewater is defined as any liquid or semi-liquid comprising organic material. In general, the invention employs the principles of anaerobic contact processing for the removal of contaminants from wastewater. Typical applications of the invention are for treating wastewaters from the grain and food processing industries, biotechnology and pharmaceutical industries, and livestock wastes; but other applications are not precluded.
In one aspect of the invention, a wastewater feed to be treated flows, preferably continuously, into a first vessel (reacting vessel) where it is mixed with anaerobic bacteria, forming an anaerobic liquor. As wastewater continues to flow into the first vessel, a portion of the anaerobic liquor, as a result of the internal pressure of the first vessel, passes into a transfer manifold and flows continuously from the first vessel into a second vessel. Because the mixer of the second vessel is off, the anaerobic bacteria, which are introduced into the second vessel, separate from the anaerobic liquor and settle to the bottom of the second vessel. Treated wastewater rises within the second vessel to a certain level where it passes into an effluent manifold. The treated wastewater then flows, preferably continuously, from the effluent manifold out of the second vessel and into an effluent conduit, where it eventually flows to a municipal wastewater treatment plant or some other like facility.
After an appropriate period of time, wastewater feed-flow into the first vessel is stopped and the mixer in the first vessel is turned off. Additionally at this time, there is no influx or efflux of fluid from either the first or second vessel so that the anaerobic bacteria of the anaerobic liquor in the first vessel separate and settle to the bottom of the first vessel.
With the influent valve of the first vessel closed, the influent valve of the second vessel is opened and the mixer in the second vessel is turned on. The incoming wastewater feed flows, preferably continuously, to the second vessel (the prior settling vessel) and is mixed with the anaerobic bacteria of the concentrated anaerobic liquor which remained in the second vessel. As wastewater feed continues to flow into the second vessel (the new reacting vessel), a portion of the anaerobic liquor, as a result of the internal pressure within the second vessel, passes into a transfer manifold and flows continuously from the second vessel into the first vessel (the new settling vessel). In the first vessel (the new settling vessel), the anaerobic bacteria separate from the anaerobic liquor and settle to the bottom of the first vessel (the new settling vessel). Treated wastewater rises within the first vessel (the new settling vessel) and passes into an effluent manifold. The treated wastewater then flows from the first vessel (the new settling vessel) into the effluent conduit where it eventually flows to a municipal wastewater treatment plant or some other like facility.
Application of the alternating anaerobic contact process can be performed with an apparatus having two or more vessels wherein each pair of vessels in the sequence provide for continuous flow from a current reacting vessel to a current settling vessel. The main aspect of the invention is that as long as there are at least two reacting/settling vessels, the alternating anaerobic contact process can be continuously applied without the requirements of an external clarifier, degassifier or other external piping and pumps between the vessels.
In yet another aspect of the invention, a multi-chambered, single-vessel system can be used wherein each chamber acts as a vessel described above. The alternating anaerobic contact process can be continuously applied between chambers of the single vessel as long as a first chamber serves as a reacting chamber while a second chamber serves as a settling chamber during a first stage of operation, and a chamber other than the first chamber acts as a reacting vessel and a chamber other than the second chamber acts as a settling chamber in a second stage of operation. An advantage of the multi-chambered, single vessel system is that only one vessel is required, thereby reducing the cost of the apparatus.